In mobile communication, ARQ (Automatic Repeat reQuest) is applied to uplink data transmitted from a radio communication mobile station apparatus (hereinafter simply “mobile station”) to a radio communication base station apparatus (hereinafter simply “base station”) in uplink, and a response signal showing uplink data error detection result is fed back to the mobile station in downlink. The base station performs a CRC (Cyclic Redundancy Check) for the uplink data, and, if CRC=OK (no error), an ACK (Acknowledgment) signal is fed back, and, if CRC=NG (error), a NACK (Negative Acknowledgment) signal is fed back as a response signal to the mobile station.
To use downlink communication resources efficiently, studies are conducted recently about ARQ, which associates uplink resource blocks (RBs) for transmitting uplink data and downlink control channels for transmitting response signals in downlink (e.g. see Non-patent Document 1). By this means, a mobile station is able to identify control channels in which a response signal is transmitted to the mobile station according to RB allocation information reported from the base station even when allocation information about the control channel is not reported separately.
Further, studies are conduct for ARQ recently whereby a response signal is spread and the spread response signal is duplicated in order to average interference of the response signal from neighboring cells or sectors and provide frequency diversity gain for the response signal (e.g. see Non-patent Document 2).    Non-patent Document 1: 3GPP RAN WG1 Meeting document, R1-070932, “Assignment of Downlink ACK/NACK Channel,” Panasonic, February 2007    Non-patent Document 2: 3GPP RAN WG1 Meeting document, R1-070734, “ACK/NACK Channel Transmission in E-UTRA Downlink,” TI, February 2007